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Further progress this afternoon: I soldered a new secondary mirror
retaining tab. Then replaced a plywood plate with a nice bit of Tufnol
for much better stiffness in clamping the secondary cage. By leaning the
OTA at 45 degrees against the workbench, re- collimation with the
Cheshire eyepiece is now a piece of cake. All thanks to the new
spider/secondary holder. When an adjustment is made it is absolutely
positive and without any "spring." Adjusting the curved spider was just
too vague for my liking. I'm hoping for the sky to clear but it is
mostly overcast. Now I must fit sights and/or a finder. No shortage of
finders but they have dovetail base fittings. I am still unsure whether I
shouldn't have finders or sights half way up the spars for easy
location from the ground.In the end I found an incredibly simple way of adding two finders without modifying or even defacing the dovetail castings. The dovetail based, stand-off stalks are hollow castings. So I just drilled a 4mm hole inside the middle of each dovetail and inserted a screw from inside the stalk itself. Both castings have a small tongue extension on the base at the closed end of the dovetail. For the larger 8x50 finder I filed a small slot in the cell for the tongue. For the smaller Vixen finder I just added a thin packing piece under the dovetail instead. Though I could just as easily have filed a slot in the cell for the small tongue and may do so anyway. After tightening a couple of nuts to lock the dovetail bases onto the cell the finders were perfectly solid. The finders have added some weight at the top of the OTA so the balance point will have moved upwards slightly. The weather was far too foul to put the OTA onto the mounting to check. When the weather is kinder, in daylight, I shall take some better pictures.
Click on any image for an enlargement.
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